Question: $ { \left[\begin{array}{rr}{0} & {1} \\ {-2} & {3} \\ {1} & {2}\end{array}\right]+\left[\begin{array}{rr}{4} & {0} \\ {0} & {2} \\ {0} & {3}\end{array}\right] = {?} } $
Answer: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{0}+{4} & {1}+{0} \\ {-2}+{0} & {3}+{2} \\ {1}+{0} & {2}+{3}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{4} & {1} \\ {-2} & {5} \\ {1} & {5}\end{array}\right]}$